Update sysrepo

There's been an API change in the C++ bindings. This change brings this
project back in sync with cla-sysrepo.

Change-Id: Ia7919e8fd413805b06c151bb83913ade0b884344
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9864ce4..1807991 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -53,7 +53,8 @@
 
 find_package(PkgConfig)
 pkg_check_modules(LIBYANG REQUIRED libyang-cpp>=0.15.111)
-pkg_check_modules(SYSREPO REQUIRED libSysrepo-cpp>=0.7.3)
+# TODO: bump to 0.7.8 once it is tagged
+pkg_check_modules(SYSREPO REQUIRED libSysrepo-cpp>=0.7.7)
 
 # we don't need filename tracking, and we prefer to use header-only Boost
 add_definitions(-DBOOST_SPIRIT_X3_NO_FILESYSTEM)